The present invention relates generally to methods for attaching parts together, and more particularly to a method for attaching first and second parts together using gas metal arc welding.
Conventional methods for attaching parts together include welding such as gas metal arc welding. Gas metal arc welding uses a consumable metal wire as one electrode and the parts as another electrode, and moves the consumable metal wire (or the parts) to draw an arc and weld the parts together. The welding is accompanied by a gas (such as a mixture of argon and carbon dioxide) to prevent oxidation and stabilize the arc. Such gas metal arc welding is well known. In a conventional gas metal arc welding technique, solid metal wire or metal core wire (i.e., an annular-solid wire whose core is filled with metal powder such as a mixture of metal, alloy and/or oxide powders) is used with the wire at a positive electrical welding potential and with the parts electrically grounded. It is known in conventional gas metal arc welding techniques to adjust the relationship between the electrical welding current and the electrical welding potential to create a sharp tip on the metal wire at the end of a weld in preparation for the start of another weld.
The conventional gas metal arc welding techniques have been employed to weld a ring to a base cup of a cylinder of a damper such as a vehicle shock absorber. Such welding is done when the base cup has been resistance seam welded to the cylinder and the cylinder filled with damping oil and possibly pressurized gas. A typical ring is a low carbon steel ring having a length of 0.5 inch, an outside diameter of 2 inches, and a thickness of 4 millimeters. A typical base cup is a low carbon steel base cup having an outside diameter of 2 inches and a thickness of 2 millimeters. Simultaneous welds are created on each side of the 0.5-inch-long contact line of the ring on the base cup by using two weld torches. These are short length, large gap welds between a thicker metal and a thinner metal. Each weld using a conventional gas metal arc welding technique is likely to have a weave shape created by moving each weld torch in a saw-tooth path to better fill the large gap. A straight-line welding path along the contact line (or even a weave welding path) using a conventional gas metal arc welding technique would not create a weldment of sufficient leg length for the required weld strength without creating too much heat in the base cup and a potential undesirable burn through. Burn through would result in the expulsion of the pressurized gas and/or damping oil in the cylinder as well as turning the cylinder, base cup, and ring into scrap.
What is needed is a method for attaching two parts together, such as a ring and a base cup of a cylinder of a damper, using gas metal arc welding which is improved over conventional gas metal arc welding techniques.
A first method of the invention is for attaching first and second parts together and includes steps a) through c). Step a) includes obtaining a metal-core consumable welding wire. Step b) includes positioning the first and second parts to create a joint line for welding the first and second parts together. Step c) includes gas metal arc welding the positioned first and second parts together using the metal-core consumable welding wire at a negative electrical welding potential relative to the first and second parts creating a weldment along the joint line.
A second method of the invention is for attaching a ring to a base cup of a cylinder of a damper and includes steps a) through c). Step a) includes obtaining a metal-core consumable welding wire. Step b) includes positioning the ring in contact with the base cup to create a joint line for welding the ring and the base cup together. Step c) incudes gas metal arc welding the positioned ring and base cup together using the metal-core consumable welding wire at a negative electrical welding potential relative to the ring and base cup creating a weldment along the joint line.
Several benefits and advantages are derived from the invention. Use of the metal-core consumable welding wire (with its powdered metal core) allows melting with lower heat input per unit weight than using solid metal cores. Having the metal core wire at a negative electrical welding potential relative to the parts causes the lighter electrons to be attracted to and strike the parts while the thousand times heavier positive ions in the arc plasma are attracted to and strike the metal core wire which results in less heat imparted to the parts than having a reversed electrical potential. The novel combination of using the metal-core consumable welding wire and the negative electrical potential of the wire relative to the parts reduces or eliminates the danger of burn through when welding parts requiring a leg length (i.e., the weldment height of the fit-up gap between two locations, one on each part, where the weldment height is substantially perpendicular to the welding length) to part thickness ratio at the weldment of at least two and allows such weld to be done with one pass along the joint line between the parts without having to weave the weld about the joint line. These large leg-length requirements are dictated by the geometry of the joint having a large gap between the parts along the weld line. A straight line weld is expected to require only half the time compared with conventional weave welds of rings to base cups of cylinders of dampers such as vehicle shock absorbers. It is noted that conventional gas metal arc welding techniques are adequate for straight line welds only when the required leg length is equal to or less than the pre-weld thickness of the thinner part.